The present invention relates to a new and improved method of casting or pouring of steel with a lower overheated or superheated temperature during continuous casting, wherein the inner surface of a tundish which is protected at all sides against radiation and equipped with at least one bottom nozzle or outlet is heated to an internal surface temperature which approximately corresponds to the steel temperature in the ladle, filled with steel and poured into at least one mold, and further the invention pertains to an improved construction of pouring vessel or tundish for the performance of the aforesaid method.
During the continuous casting of steel the melt flowing out of the transport ladle is poured through a tundish into the continuous casting mold. The tundish undertakes the following functions: destruction of the flow energy which prevails at the ladle casting jet, generating as uniform as possible inflow of steel into the mold, elimination of slag and gas from the melt, distribution of the steel into a number of molds, and so forth.
Owing to the use of tundishes during continuous casting operations part of the overheated thermal energy of the steel is consumed. This overheated thermal energy, as a general rule, is introduced into the steel production assembly in order that the steel, during the continuous casting operation, possesses the desired casting temperature and to insure, for instance, that the pouring nozzles do not freeze.
In order to prevent cooling of the steel flowing into the tundish it is known to pre-heat the same prior to the start of casting at a pre-heating station. In this regard there is provided at the inner surface of the lining a pre-heating temperature of about 1200.degree.C. As experience has shown the temperature of the steel in the ladle, depending upon the size of the ladle and the tundish, must be at least about 50.degree.C higher than the desired casting temperature in order to provide for a disturbance-free casting of the melt. However, producing steel with a high tapping temperature, on the one hand prolongs the steel production process and, on the other hand, reduces the service life of the lining in the steel production assembly, thereby lowering the efficiency of such assembly. In addition to such disadvantages there also can be brought about metallurgical drawbacks, such as, for instance, the migration of phosphorous from slags containing phosphorous back into the steel bath and so forth. Moreover, these tundishes must be manually cleaned of slag and solidified residual steel in a complicated and time-consuming manner after each pour, further they must be repaired and then again heated-up from their cooled condition.
Continuing, a tundish has become known to the art which is equipped with an electrical graphite rod- resistance heating device arranged at the cover of the tundish. Such heating device is employed to pre-heat the inner surface of the tundish up to about the temperature of the steel in the ladle and to maintain the steel in a heated condition during casting. Equipping a continuous casting plant with such pouring vessels or tundishes, however, requires additional investment costs as well as also additional maintenance- and operating costs for the heating devices. The provision of current infeed devices and cooling water circulation systems for the heating devices complicate the economies of the tundish. The accessibility and the operational reliability of the continuous casting installation is likewise impaired. Also due to the installation of the heating element in the cover of the tundish the latter and the continuous casting installation undesirably increase in size by about 60 to 80 centimeters. In the case of tundishes which have been used and cooled, there occurs during the pre-heating of the inner surface to approximately the casting temperature an additional drawback because the slag which remelts and the steel residues which again remelt or liquify tend to clog the nozzles or openings at the floor of the tundish.